1. Field of the Invention
The present invention relates to an auto focus adjustment apparatus including a defocus amount detection unit configured to detect defocus amounts, and relates to an image pickup apparatus equipped with the auto focus adjustment apparatus.
2. Description of the Related Art
In the auto focus adjustment apparatus of a general inter-changeable photographing lens type single reflex camera system, a camera and an interchangeable photographing lens (hereinafter referred to as photographing lens) each incorporate a micro processing unit (MPU) individually to communicate mutually, and thereby the camera and the photographing lens function as a whole. To put it concretely, the camera MPU controls a sensor for detecting a defocus amount for focus detection, and the lens MPU transmits an optical focusing correction value of each photographing lens to the camera MPU to perform the optimum focus detection of each photographing lens.
It is conventionally publicly known to store adjustment values for auto focus adjustment in a camera and a photographing lens beforehand, which is the so-called focus adjustment. To put it concretely, the individual difference of each product due to tolerances or the like of using parts at the time of production is detected in a calibration process, and the adjustment values corresponding to individual operation characteristics are stored in a nonvolatile memory at the time of a factory shipment beforehand to make the camera and the photographing lens perform proper operations at the time of photographing on the basis of the adjustment data.
On the other hand, it is known that there is a possibility of a shift of the focusing position if a strong impact is applied to the camera and the photographing lens owing to their falls and the like after their factory shipments. Moreover, if a quick return mirror or the like is used an optical path formed by an optical system from photographing lens to a sensor for detecting a defocus amount, the angle of the mirror gradually varies every opening and closing of a shutter, and thereby a focusing position sometimes gradually deviates as a result.
At a time like this, it is better to bring the photographing lens or the camera into a service center of a manufacturing company, and to have the adjustment value in the nonvolatile memory of the photographing lens or the camera updated with a dedicated adjustment tool. Because the places where the service centers exist are limited, there is the problem of loss of swiftness.
To this problem, for example, Japanese Patent Application Laid-Open No. 2001-174690 discloses to make a camera hold a correction value different from the adjustment value set in a calibration process in a factory, and to be equipped with a unit for allowing a photographer to freely change the correction value. That is, Japanese Patent Application Laid-Open No. 2001-174690 discloses the technique enabling a photographer to freely correct the focus adjustment and to freely return the setting to that at the time of the factory shipment of the camera.
Japanese Patent Application Laid-Open No. 2001-174690, however, discloses only one different correction value, that is, a correction value having a constant value, indicating a single correction. On the other hand, more strictly speaking, the correction value that makes a focus optimum differs depending on a focus areas, an object light to be used for defocus amount detection, a distance ring position of the photographing lens, a zoom position in case of a zoom lens, a light source illuminating an object, a temperature, and the like, for each photographing lens. Moreover, this dependency differs with each photographing lens. In detail, the focusing deviations of some photographing lenses depend sensitively on their zoom positions, and the focusing deviations of some cameras depend sensitively on temperatures. The total focus shift including all correction factors that causes these focus shifts are designed to be within the so-called permissible circle of confusion of a camera system, which causes no practical problems as a product standard, and the total focus shift is adjusted in the calibration process in a factory.
On the other hand, in a recent digital camera, it is possible to enlarge only a part of a photographed image to any extent to display the part by a simple operation especially in the case of displaying the photographed image on a display of a personal computer. Because this sort of operation is not for appreciating the whole photographed image, the focusing accuracy equal to or higher than that in the permissible circle of confusion is required. As a result, there is a possibility that some viewers feel a part of an enlarged photographed image to be out of focus when looking at that part.
A camera system having a focusing deviation within the permissible circle of confusion by any way of appreciation should ideally be designed, and the focusing deviation should be adjusted in the calibration process thereof in a factory. However, if the focusing accuracy thereof is excessively raised for an industrial product that is manufactured in a large quantity, such as a camera, this remarkably increases the manufacturing cost of the product and results in a very expensive product.